Mineral wool



United States Patent 3,154,463 MENERAL WUUL Olof Kjell-Berger, Skovde, and Eric Grane, i ersherg,

Skovde, Sweden, assignors to Rockwool Alrtieholaget,

Skcvde, Sweden, a corporation of Sweden No Drawing. Filed Dec. 7, 1959, Ser. No. 857,504

Claims priority, application Sweden Dec. 29, 1958 3 Claims. (Cl. 161-469) The present invention relates to mineral wool, and more particularly, to mineral wool having a distribution of fibers of varying thickness in order to fulfill two functions, namely good heat insulation and resistance against sinking.

In this connection, mineral wool shall be understood to be in an inorganic, fibrous wool-like material, produced in an artificial manner and made of glass, stone, slag or similar siliceous stuffs or compounds. Wool of the type here intended may be made by melting down the raw material at a high temperature and producing solid fibrous structures from the melt.

In practice, the production of such fibers may be done in several different ways. The conventional method has been to convert the melt into fibers by the influence of an air jet or high pressure steam (the blowing method). In recent years, new methods have been developed for fibra-tion of the mineral melt. For example, melt may be transferred to rotating means such as discs, wheels or the like, which are put in rotation with a high speed so that the melt transferred to said rotating means is thown out by the centrifugal force in the form of fine fibers (the spinning method). A further proposal has been to transfer the melt into continuous fibers by pressing it through fixed nozzles of metal or ceramic material (the pressing method).

Wool produced according to the first method (the blowing method) or according to the spinning method shows a circular cross-section of the separate fibers but has a rather widely varying diameter of fibers. Wool produced according to the pressing method has a unitary fiber diameter. As a rule, the fibers will also be circular in cross-section.

Dependent upon which one of the three methods is used, certain characteristic differences with regard to the percental distribution of fiber length as well as fiber diameter will result, and this percental distribution may furthermore be influenced by other factors such as choice of the temperature of the melt and its chemical composition, choice of pressure and speed of the air or the steam,

choice of peripheral speed and diameter of the spinningwheels, and so on.

Mineral wool of the kind here described has found a wide use as an insulation means against heat and cold. The heat transfer through a mineral wool mass, for instance through a mat of mineral wool, mainly takes place in four different ways, viz. (1) by conduction in the air, (2) by conduction in the material, (3) by convection, and (4) by radiation. Consequently figures determined with respect to the sum of all of these four components of heat transfer should be regarded as a material constant valid for the mineral wool. The heat conduction figure is, according to practice, stated in the form of the amount of heat in kilogramcalories, transferred during one hour through a layer of mineral Wool, one meter thick and one square meter in surface area with the difference in temperature between the two surfaces of the layer being 1 C. From this, it will be evident that the lower the heat conduction figure of a given mineral wool, the better the heat insulating property of the mineral wool.

The present invention is based upon extended investigations of determining how the different components of "ice heat transfer vary with the dimension distribution of the fibers contained in the mineral wool.

The magnitude of the heat transfer through radiation is determined by the color of the wool material, the character of its surface, and of the distance between the fibers. With maintained weight volume of the mineral Wool, the distance between the fibers will mainly be given, and neither the color, nor the character of the surface of the separate threads or fibers can influence this contribution to an essential degree. Therefore, one cannot essentially influence the component of heat transfer power through radiation.

The magnitude of the component of heat transfer, which is dependent upon conduction through the air, will, with regard to normal mineral Wool, be rather important, as the mineral wool normally contains between and 98% air. At constant temperature and Weight volume of the mineral Wool, however, this component can not be influenced to an essential extent, and it can be said to be almost constant.

In a blown or spun mineral wool, the fibers are rather evenly distributed in all directions, and practically no fibers run straight through an insulation body made of mineral wool, e.g. a mineral Wool mat. The consequence is that the component of heat conduction through the solid material in the mineral wool must, due to its nature, be very small, and that it will therefore be of no decisive account for the whole. Certainly, the separate mineral wool fibers are in contact with each other, and a heat conduction over a plurality of fibers would be possible with interconnected contact points. But because the contact points are mainly point-formed, due to the circular cross-section of the fibers, such heat conduction will not influence the total heater transfer to an essential degree.

Thus, the contribution by own convection of heat inside the material remains for consideration. Investigations have proved that this component is practically the only one that may be influenced to an essential degree, as long as the volume weight of the material is predetermined. Investigations have also shown that this component of heat transfer has often assumed a dominating order of magnitude, and therefore, it is both important and possible to improve the heat insulation properties of the mineral wool substantially by decreasing the convection component.

The convection current resistance against air through a mass of the common kind to which the mineral wool belongs, follows definite although not fully explored laws. It may be stated, however, that it depends very highly upon the diameter of the fibrous material. As a principle one may reduce this problem into a resistance against current, caused by the circularly cylindrical body, existing in an angle to the direction of the current. From hydrodynamics and aerodynamics, it is known that the current resistance executed by such a body is proportional to the diametrical surface of the body. Investigations with mineral wool have shown that the convection resistance is practically directly proportional to the fiber diameter, provided that the fibers have been compressed into constant weight volume. The following values may be mentioned: At tests with fibers which were spun down to between 1 and 4a, a given convection resistance was obtained in the mineral Wool mass, the percentage of mineral wool being 1% and which, consequently, contained 99% air. When mineral wool which had been spun to a diameter within the interval between 4 and 8 was used, 2.4% fibers and 97.6% air were required for the same convection resistance, and when mineral wool material which had been spun down to a diameter of 8 to 16 was used, 4.8% mineral wool and 95.2% air were required for the same convection resistance.

These investigations have proven that for obtaining the best possible heat insulation figure in a mineral wool mass, fibers of the smallest possible diameter should be used. But this is impossible to follow in practice, because the insulation material must be subjected to the strain normally occurring at the production, transportation and finally the mounting stages. Moreover, the insulation material thereafter must be able to resist thermic movements and the like. It has been proven that the fiber diameter cannot be decreased to a value which would be satisfactory from insulation point of view, without simultaneously causing the mineral wool mass in the insulation body to become so brittle and soft that it will sink together under the strain. The fibers consequently become deformated and a packing of the fiber material takes place,

while insulation properties at the same time are seriously impaired.

The present invention is based upon the observation that the insulation figure is only influenced to a small degree by the given part of the fibers having an essentially greater diameter than the remaining ones. The low value of the heat transfer by conduction in the solid fiber material, and the heat conduction figure is mainly determined by the smallest diameter of the fibers, as long as the quantity of these fiber with small diameter does not exceed a given percentage of the total fiber mass. Therefore, the tests were directed upon stating the limit values for the quantity and diameter of fibers of smaller diameter, in order to obtain the lower heat conduction figure. Extensive tests with all kinds of fiber compositions of varying diameters gave finally the result that the fiber diameter should be rather continuously variable from about I and up- Ward to a value dependent upon the character of the material. The magnitude of this value is dependent upon the tendency of the material to form pearls rather than fibers. For instance, regarding glass which will practically not at all form pearls, the minimum value of the fine material wool should be 7%, but regarding rockwool, viz., fibers made of stone, this value is about 10% up to 15%. Thus, at least this percental share of the total fiber quantity is the fine material wool having a diameter that is less than 4 A fibrous mass with this specific composition, independently of how strongly it is compressed, will be of no worse insulation quality than fiber masses composed entirely of fibers with extremely small diameter, but it will obtain a strength against breakdown and compression of the fiber mass. Therefore, insulation bodies built up from the fibrous mass will be constant as to their volume. As an explanation, the fibers with greater diameter serve as a reinforcement of the total fiber mass, thereby protecting the fibers of small diameter from being broken down, whereas the fibers of small diameter, by their great convection decreasing action, prevent the emanation of substantial convection current of the air in the interior of the mass.

What we claim is:

l. A fibrous wool-like mass of mineral wool for use as heat insulation consisting of air and fibers of a siliceous material selected from the group consisting of glass and stone with the air comprising 95 to 98 percent of the mass, said fibers being of various diameters ranging upwards from about 1 micron, the fibers of the diameter from 1 to 4 microns comprising at least 7 percent by weight of the entire fiber content of the mass.

2. A fibrous wool-like mass of mineral wool for use as heat insulation consisting of air and fibers of glass with the air comprising 95 to 98 percent of the mass, said fibers being of various diameters ranging upwards from about 1 micron, the fibers of the diameter from 1 to 4 microns comprising at least 7 percent by weight of the entire fiber content of the mass.

3. A fibrous wool-like mass of mineral wool for use as heat insulation consisting of air and fibers of stone with the air comprising 95 to 98 percent of the mass, said fibers being of various diameters ranging upwards from about 1 micron, the fibers of the diameter from 1 to 4 microns comprising between 10 and 15 percent by wei ht of the entire fiber content of the mass.

References Cited in the file of this patent UNITED STATES PATENTS 2,188,373 Pearce Jan. 30, 1940 2,641,028 Steele June 9, 1953 2,721,139 Arledter Oct. 18, 1955 2,841,858 Owens July 8, 1958 2,919,211 Labino Dec. 29, 1959 2,962,415 Arledter Nov. 29, 1960 OTHER REFERENCES Materials in Design Engineering, August 1958, pages 1 11, 112. 

1. A FIBROUS WOOL-LIKE MASS OF MINERAL WOOL FOR USE AS HEAT INSULATION CONSISTING OF AIR AND FIBERS OF A SILICEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF GLASS AND STONE WITH THE AIR COMPRISING 95 TO 98 PERCENT OF THE MASS, SAID FIBERS BEING OF VARIOUS DIAMETERS RANGING UPWARDS FROM ABOUT 1 MICRON, THE FIBERS OF THE DIAMETER FROM 1 TO 4 MICRONS COMPRISING AT LEAST 7 PERCENT BY WEIGHT OF THE ENTIRE FIBER CONTENT OF THE MASS. 